Smokeless shotgun-powder



F. DU PONT. SMOKELESS SHOTGUN POWDER.

APPLICATION FILED MAY 28, I919.

Patented Nov. 15, 1921,

1 76.3. //VVE/V7'0/? Francis J. den/ arn.

W/TNESS: @7742.

II'TWFMSK FRANCIS I. DU FONT, OF WILMINGTON, DELAWARE.

SMOKELESS SHOTGUN-POWDER.

Application filed may 28,

To all whom it may concern:

incorporation of wet nitrocellulose with salts, formation into grains, preliminary drying, spraying with a solvent, and final drying. Marshall on E azplosi'ves, vol. I,-page 324, sets forth this process with some particularity and specifiesin detail the steps that are usually practised. The wet nitrocellulose, which may be 40 per cent. water, is mixed with salts, which may be barium and potassium nitrates in known propor-' tions. For example, the proportions may be 85 parts nitrocellulose calculated to the dry weight, 10 parts barium nitrate and five parts potassium nitrate. The ingredients are ground together in a mill, such as a wooden barrel with hard wood balls, or the incorporation may be performed under edge runners similar to those used for the milling of black powder, as described by Marshall. The material is then passed through a sieve. The moist grains are, in the best practice, spread on trays and dried by means of a current of hot air. The material is then allowed to cool. The necessary and important step of hardening, by treating with a solvent, is usuall performed by spraying. Marshall descri es the known process of spraying the material while it is inside an hermetically closed rotary drum. The powder is then allowed to steep in the same vessel or in another one, and is subsequently dried.

The main objection to known processes, of which the foregoing described process is typical, resides in the hardening step of the process. The grains, after they are formed and dried, are tender and cannot stand much friction. It is difficult or impossible to distribute the solvent uniformly. If too much solvent is received in one place, the grains coalesce into lumps. Again, if some of the grains et little or no solvent, they remain mechanically unstable and are easily broken up in the subsequent handling or use of the Specification of Letters Patent.

Patented Nov. 15, 1921.

1919. Serial No. 300,266.

powder. With the best handling, lack of uniformity in the distribution of the solvent gives some difference in characteristics between the' grains which have received more solvent than they should and those which have not received as much as they should, making a product which is not quite uniform. I

While my process involves, by preference, some variation in detail in' the grain-forming step, the essential feature of my process comprises a substantially new hardening or solvent-applying process whereby the difiiculties and objections of known processes are avoided. The invention will be best understood if I describe the operation, including known steps, in connection with the accompanying drawings, which are diagrams of the main apparatus, although it will be understood that my invention is not, limited to the employment of any particular mechanism.

Figure 1 is a sectional view of the incorporating drum.

Fig. 2 is a side elevation of the grainforming apparatus.

Fig. 3 is a diagram of an apparatus which may be used in the hardening process.

The ingredients are incorporated in the rotary drum (1. containing the hard wooden balls 6. The material is then rubbed through a sieve c with meshes approximately the same as, or slightly larger than, the desired size of the grains. This sieve projects into the end of a revolving cylinder d, which should be of considerable size, say thirty inches in diameter or more. This cylinder is open at both ends-and slightly inclined. Upon rubbing the wet nitrocellulose mixture through the sieve, particles fall down upon' the revolving surface and are rolled immediately into grains, having a more or less round shape. This grained material then runs out from the other end of the cylinder, and is dried in some kind of a drying apparatus which does not keep the grains in motion. An ordinary tray dry house will answer. The reason the material is not to be kept in motion, during drying, is that the grains which have been formed when the nitrocellulose is wet would be disintegrated by friction upon one another after the material is dried.

The powder is now ready for the hardening process. I immerse the same completely in a mixture of a substance of relatively high boiling point, which is a. solvent of nitrocellulose, with a substance of relatively low boiling point, which is not a solvent of nitrocellulose. I use these two substances in such proportions that the mixture will not gelatinize nitrocellulose, or at least will not gelatinize it to an extent which willcause the grains to coalesce.

A preferred mixture is two parts by weight of carbon tetrachlorid (a non-solvent), which has a boiling point of about 76 degrees 0., with one part of amyl acetate (a solvent), which has a boiling point of approximately 148 degrees (1- These substances are perfectly miscible.

Having drained ofl the excess-of the mixture, I then subject the grains to a recovery process in which a current of warm air passes over the mass while it is kept in motion. This I do in a revolving drum connected with a circulating fan, a heating coil and cooling coil, '11 a manner quite similar to that WlllCl'l has'lneen applied to solvent recovery. in the past. The apparatus shown in Fig. 3-will be effective. f represents the revolving drum, 9 the fan, It heating coils, i an outlet pipe from the drum, and j cooling coils.

What takes place in the recovery process is that the material of the lowest boiling point, or the non-solvent, which up to this time has interfered with the solvent acting upon the nitrocellulose, isdriven ofi' first, leaving the grains evenly moistened with the substance of higher boiling point, which is a solvent of nitrocellulose. In the example given, the carbon tetrachlorid is driven off first. At this point the colloidization of the nitrocellulose takes place and the grains are fixed. The recovery process then continues by the application of more heat, and the removal of the solvent proper takes place,

leaving the grains finished.

By using the air circulating process, on account of the high vapor tension of both carbon tetrachlorid and amyl acetate, the re covery takes place at temperatures below the boiling points of these substances, so that it is not necessary everto heatthe powder very hot in the recovery process. An initial heat of about 35 degrees C. raised'gradually to about 60 degrees C. will sufiice If there is a great difl'eren'ce between the boiling points of the two substances, as in the case of those mentioned, it isquite easy to separate them.- Moreover, if the two substances, as in the examples given, have widely different specific gravities' (carbon tetrachlorid 1.58, amyl acetate 0.866), the exact "proportions of the mixture may be ascertained by determining its specific; .gravity, and thus may be corrected any errors of proportion in the recovered ma- 'terial that may have resulted from the loss of the more volatile ingredient.

Having now fully described my invenby etters Patent is:

1. The process of making smokeles shot gun nitrocellulose powder which comprises incorporating the ingredients, forming them tionlz what Iclaim and desire toprotect into grains, treating them uniformly with a mixture of substances having different boiling points, one of which is a substance which, in a liquid condition at normal pressure and at a temperature below the ignition point of the nitrocellulose, is itself an active solvent of nitrocellulose but will not combine therewith to form a chemical compound, and the other'of which is a liquid that is miscible with said solvent and not a solvent of the nitrocellulose, and then driving off the nonsolvent, whereupon the nitrocellulose is colloided and the grains are fixed.

2. The process of making smokelessshot gun nitrocellulose powder which comprises ncorporating the ingredients, forming them into grains, treating them uniformly with a 

